Pilea White/Brown/Black Spots on Leaves (Causes and Cures)

Pilea peperomioides are generally quite hassle-free house plants, but like any plant, they are susceptible to certain leaf problems.

One that can be a little confusing, is their tendency to occasionally develop white spots on the underside of their leaves.

They are not particularly favored by common pests, and other than mold, are normally disease-free.

With a little bit of knowledge and some gentle nurturing, none of these issues are difficult to overcome.

Pilea White, Brown, Black Spots that look like tiny scabs are a result of Edema, pest infestation, diseases, or incorrect watering. If left unaddressed, this problem can become severe. The good news is that it is really very simple to overcome this problem and your plant will soon bounce back.

How to Identify Pilea White/Brown/Black Spots

What some gardeners might find confusing, is identifying the problem from which their Pilea is suffering.

The white spots may take the form of small pimple-like dots beneath the leaves, a pale discoloration on the leaf itself, or even a white powdery substance that one could easily associate with flour or baking soda.

Very often, these different symptoms are collectively referred to as white spots, where in fact, they may not be spots at all.

You will find brown or black spots on the older leaves first. It indicates that the root system is severely damaged and fungal diseases are already affecting your pilea.

On the other hand, brown and black spots can also be caused by direct sunlight or sunburn.

Why Does Pilea Have White, Brown, Black Spots?

The reason for these different leaf conditions can be quite varied, and as one would expect, different symptoms apply to different problems.

Although the problems may vary, very often the same treatment will cure a number of symptoms so don’t worry if your diagnosis is not exact.

The easiest way to get to grips with this is to break each problem down individually so that you are easily able to diagnose what the problem is and then to take the appropriate action.

Edema

Edema is a problem that is associated with overwatering or not enough light. The most common symptoms manifest themselves as crusty white spots on the underside of the leaves.

Left unaddressed, these can eventually lead to the death of the leaf tissue in a process that is known as necrosis.

In effect, what is happening is that the plant is not able to transpire effectively.

Its pores become blocked, and that is when the white blemishes or scabs are formed.

Solution:

The first step toward correcting this problem is to stop watering and to move the plant into a position where it receives bright light, but not direct light. Allow the potting soil to dry out completely and then soak the plant until water runs through the hole in the bottom of the pot.
After that, do not water the plant again until the top one inch of the soil has tried out completely. Using this method, your plant will probably only need to be watered once per fortnight. That will obviously be dependent on local weather conditions, as well as the temperature at which you keep your home.
Never leave your Pilea standing in a saucer of water, which will delay the training process.

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Powdery Mildew

This is quite an easy issue to identify. Your plant will begin to look like someone has given it a light dusting with icing sugar.

If you are paying close attention to your plant, you are likely to spot this early, when it will only have affected a few leaves, and perhaps the base of the stems.

If you have not been diligent in doing your plant inspections, that magic fairy dust can soon engulf the whole plant.

This is a problem that can move very quickly, so you need to take action before other plants become infected by the airborne spores.

Solution:

Immediately wipe down the plant with a slightly damp cloth which should remove all visible signs of the spores.
Isolate it from all other plants.
Make sure that the plant is in a position where air circulation is good.
Make sure that the plant is getting enough light, but no direct sunlight.

Excess Light

With all houseplants, it is important to get the lighting correct, and this is particularly true of your Pilea.

Remember that you are looking for a position with plenty of sunlight but not direct sunlight, which will sunburn the leaves.

One of the tell-tale symptoms of excess light is the curling of the top leaves of this plant.

Solution:

If you suspect that your Pilea is receiving too much light then obviously, the first thing to do is to move it to a spot where the lighting is less direct. This plant is more tolerant of low light than it is of excess light. If you are unsure if it is in too bright a spot, err on the side of caution and go for a position that is more shaded. Normally a west or northwest-facing windowsill makes an ideal spot.
If the plant is not receiving enough light, and I want to stress that this is less common than too much light, the leaves will curve outwards in what is known as doming.

Temperature Stress

Because we know that this plant originates in southern China, we understand that it requires a moderate temperature in order to thrive.

Between 60 and 80°F (15-30°C) is an ideal range within which to cultivate this plant.

A clear indication that the plant is becoming heat-stressed is that the leaves will begin to curl inwards in a manner known as cupping.

Solution:

Generally, the first thing to do, if you suspect that it is the temperature that is stressing your plant, is to get hold of a thermometer and find exactly what the temperature range is in the plant’s vicinity.
Most garden centers will be able to sell you a thermometer that will record both the maximum temperature achieved, and the lowest temperature reached.
If you cannot achieve the desired temperatures in the room that the plant is housed in, you may need to find a more suitable position in another room. Bear in mind the fluctuations brought about by central heating, especially in the winter months.
When you locate a position where the ideal temperatures can be maintained, leave the plant in that position. These plants do not like to be moved too frequently.

Pest Infestation

A healthy Pilea has leaves that are coated in a waxy cuticle. In general, this will act as a good deterrent for most pests.

When a plant is weakened by some other factor, the cuticle ceases to be as thick and that is often when the plant is at its most vulnerable.

That is not to suggest that these plants will never be attacked by pests, but with a healthy plant, it will very rarely become an issue.

Two pests that you may encounter are thrips and aphids. Both of these are sap-sucking insects. Symptoms of their attack are small, pale blemishes where the creature bites into the leaf.

You may also notice distortions in the shape of the leaf or small, round bumps. Fortunately, both insects can be dealt with in the same manner.

Solution:

Initially, you need to check your diagnosis by looking for the culprits. Aphids that attack Pileas are small and white and may look like a white powder. Thrips are tiny narrow black insects.
One good piece of advice is to thoroughly inspect a plant before purchasing it. These pests may well have invaded the plant while it was in the nursery or florist.
If you spot one of these insects on your plant, you can often prevent further infection by wiping the leaves and stems with a damp cloth.
In the event of the infestation is severe, use an insecticidal soap or neem oil to wipe the leaves with.
Remove badly damaged leaves with scissors or secateurs.

The one other pest that may decide to put in an appearance, is scale insect.

This is another of those pesky sapsuckers and they love to hide out in the leaf and stem nodes, particularly towards the base of the plant.

They look like green bumps or warts. If spotted early, they can simply be scratched off the plant with a fingernail or the blade of a knife.

Solution:

They are well disguised so keen observation is a must.
Scrape them off when the infestation is not too serious.
If there are a lot of them, dip a cotton ear bud in spirit alcohol and wipe them off with that. Don’t just wipe the whole leaf with alcohol on a cloth. This can damage the waxy outer layer.

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Fungal Diseases

Gray mold (Botrytis)

This is a common fungal disease in houseplants, but fortunately, it is a disease that does not often occur on Pilea. It is identified as a grey bull’s-eye-shaped mark on older leaves.

It frequently starts by developing on dead plant material left at the base of the plant. By simply practicing good plant hygiene, this problem can be avoided. (Source: Penn State University)

Solution:

Use good watering practices and don’t allow the plant to stand in damp potting soil.
Water the plant early in the morning so that it has plenty of time to dry out during the course of the day.
Ensure that there is good air circulation, as fungal diseases thrive in stagnant air.
Once you spot the disease, cut away any of the infected leaves and dispose of them carefully.
Ensure that the humidity levels around the plant are not too high.
As a last resort, if the infection becomes severe, spray the plant with a fungicide that you will be able to obtain at your local garden center.

White Mold (Saprophytic fungus):

This fungus is normally first noticed when you see a white weblike substance growing on the surface of the potting soil.

It seldom proves fatal to your plant, but you should treat it as an indication that the growing conditions are not ideal.

If you don’t take action timeously, you risk other health problems coming into effect.

In other words, you should treat this particular mold as an early warning system.

You can get rid of it by simply scraping it away with a knife or spoon, but understand that you will have cured the symptoms, but not the cause.

Solution:

The most likely problem here is that you are overwatering your plant. This mold thrives on the surface of damp potting soil.
Always allow the top inch of potting soil to dry out between waterings.
Make sure that the hole in the bottom of the pot is large enough to allow water to drain away freely.
Decrease humidity.

Fertilizer Problems

Overfeeding your Pilea may result in small white dots developing on the underside of the leaves. They look like tiny grains of sugar.

This is frequently the result of overfeeding. Chemical salts in the fertilizer, or from tap water, may block the pores, (known as stomata in plants).

Solution:

Use a balanced liquid house plant feed, but with the Pilea, you must use it in moderation.
Feed your plant just once per month between late spring and mid-autumn. During the cooler months stop feeding altogether.
Avoid using municipal tap water and try to use harvest rainwater or use sterilized water instead.

Poor Air Circulation

Stagnant air is a surefire recipe for many health problems, and particularly for the transmission of fungal diseases.

While no houseplant appreciates being kept in a draft, it is still important for air to be able to circulate freely.

One of the most likely symptoms of poor circulation is the appearance of fungal diseases.

Solution:

When the outside temperature has warmed up, open a window and leave it open for a few hours of the day.
Don’t crowd this plant among too many other plants, as this will decrease the amount of air that is able to circulate.

Incorrect Watering

Here we come to what is probably the most common cause of house plant demise among all houseplants.

Incorrect watering quickly leads to a number of different types of health problems. Such as spots on pilea leaves, yellowing and leaves dropping or falling off. And you can avoid these easily by following the steps below.

Solution:

Ensure that the container that your plant is potted into has sufficient drainage holes in its base.
Water thoroughly from the top downwards, and then allow the water to finish draining before placing the pot back in its saucer.
Apply the water to the soil surface without wetting the leaves, as this encourages disease.
Do not water until the top inch of potting soil has dried out. You can check this by poking your finger into the soil up to your first knuckle.
During the winter months, reduce watering considerably, and pick it up again once the growing season starts in early spring.
Try to use distilled water or capture some rainwater, as this is chemical-free.

Potting on

One common mistake that newbie houseplant owners frequently make is to place their plant into too big a container.

This is an easy error to make, and one that stems from the mistaken belief that the more soil your plant has available, the happier it will be and the quicker it will grow.

In reality, when you plant your Pilea into a much bigger container, it is surrounded by a thicker layer of soil. This will act like a sponge.

Instead of draining quickly, the plant is surrounded by a soggy layer of wet soil and this can cause root rot and facilitate the development of mold and other diseases.

When you first purchase a plant, tip it out of its container and ensure that it is not root bound.
If it is root bound, repot it, but only into the next size container. If it is not root bound, then leave it in its existing container.
After that, only pot a plant on when its roots totally fill the container that it is growing in.
Use a good proprietary potting compost.

Frost

Frost is one thing that will quickly kill your Pilea. If you live in an area that suffers from harsh winters, you may think that a plant that is grown indoors is not susceptible to this problem.

It may seem relatively warm in the house, but that may not be the case if your plant is standing near a window where the temperatures may be far lower than other areas of the room.

Frost causes the cells of the plant to expand and then burst, often with fatal results.

Frost damage exhibits itself in the form of black soggy patches on leaves and leaf tips, quickly followed by the demise of the remainder of the plant. It normally affects young, new leaves first.

Solution:

It is difficult to cure a frost-damaged plant, so avoidance is the best form of action.
In the event of minor frost damage, the plant may well recover if it is moved to a warmer position.
Don’t place your plant near a window in the coldest months.
Avoid drafts.
Use that thermometer to check just how low temperatures are getting overnight.

Final Words

Those white, brown, or black spots might look like scabs, or like tiny grains of salt. The scabs relate to Edema, and the salt specs, to excess fertilizer or chemicals in the water.

Both are issues that are within your control. The correct watering technique, bright lighting, and good ventilation will prevent almost all of the problems we have just looked at.